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Junction formation and current transport mechanisms in hybrid n-Si/PEDOT:PSS solar cells

: Jäckle, Sara; Mattiza, Matthias; Liebhaber, Martin; Brönstrup, Gerald; Rommel, Mathias; Lips, Klaus; Christiansen, Silke

Volltext ()

Scientific Reports 5 (2015), Art. 13008, 12 S.
ISSN: 2045-2322
Deutsche Forschungsgemeinschaft DFG
SFB 951
Hybrid Inorganic/Organic Systems (HIOS) for Opto-Electronics
Deutsche Forschungsgemeinschaft DFG
Cluster of Excellence 315; Engineering of Advanced Materials
Bundesministerium für Bildung und Forschung BMBF
03SF0403; SISSY
Silicon Insitu Spectroscopy at the Synchrotron
Zeitschriftenaufsatz, Elektronische Publikation
Fraunhofer IISB ()

We investigated hybrid inorganic-organic solar cells combining monocrystalline n-type silicon (n-Si) and a highly conductive polymer poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS). The build-in potential, photo- and dark saturation current at this hybrid interface are monitored for varying n-Si doping concentrations. We corroborate that a high build-in potential forms at the hybrid junction leading to strong inversion of the n-Si surface. By extracting work function and valence band edge of the polymer from ultraviolet photoelectron spectroscopy, a band diagram of the hybrid n-Si/PEDOT:PSS heterojunction is presented. The current-voltage characteristics were analyzed using Schottky and abrupt pn-junction models. The magnitude as well as the dependence of dark saturati on current on n-Si doping concentration proves that the transport is governed by diffusion of minority charge carriers in the n-Si and not by thermionic emission of majorities over a Schottky barrier. This leads to a comprehensive explanation of the high observed open-circuit voltages of up to 634 mV connected to high conversion efficiency of almost 14%, even for simple planar device structures without antireflection coating or optimized contacts. The presented work clearly shows that PEDOT:PSS forms a hybrid heterojunction with n-Si behaving similar to a conventional pn-junction and not, like commonly assumed, a Schottky junction.